Automatic synchronization of two strip drives

ABSTRACT

A process of synchronizing first drive means for moving a first strip and second drive means for moving a second strip comprising the steps of operating the first drive means to move the first strip having a first signal recorded thereon on predetermined length portions and reproducing the first signal from the first strip as the latter is thus moved, operating the second drive means to move the second strip, and generating a second signal in response to the movement of the second strip. Providing with each of the first and second signals at least one varying parameter, at least in portions of the signals which are associated with predetermined length portions of the first and second strips, respectively, which parameters have a predetermined functional relationship to each other, comparing the first and second signals to produce a control signal, and controlling one of the first and second drive means to maintain the control signal at a predetermined value, indicating a synchronous movement of the two strips.

[ 1 3,722,987 51 Mar. 27", 1973 United States Patent 1 Cap et a].

X wX. HKHUU /55/ 2332 5 u Us m m3 m m w a u en m m mim fhe ve3 S mam m .l t as, v a n 911 VG an; my llll i WMWW mmm xE v 2268 2 6495 in $3 mn Z9138 r 67488 MM v i HS! 3333 PAA h df F m r 0 b. m n a N mm 0 mw r a I m n T M .Mn A was.. Z .l v .l m .& N a m 0 J wfi R 9 H f? m CE C V M Y k d C i eam e o u T HoVSW A M 5 v s O o t T m Uw m I W M H [57] ABSTRACT A process of synchronizing first drive means for moving a first strip and second drive means for moving a second strip comprising the steps of operating the first Austria [73] Assigne'e: Karl Vochenhuba; Rairnnnd I-iauser,

bq h q .v n e [22] Filed: June 25, 1971 [21] Appl. No.: 156,626 drive means to move the first strip having a first signal recorded thereon on predetermined length portions 1 v and reproducing the first signal from the first strip as Fm'elgn pll Dita 'the latter is thus moved, operating the second drive June 25, 1970 July lO, 1970 July 10,1970

means to move the second strip, and generating a Austria... second signal in response to the movement of the vsecond strip. Providing with each of the first and Austria...

Nov. 11, I970 Austria....................................l0l66 second signals at least one varying parameter, at least [52] U s CI, in portions of the signals which are associated with predetermined length portions of the first and second [51] Int. 31/04 strips, respectively, which parameters have a predeter- Field of Selrch............352/5, 12,15,16, 17,18,

mined functional relationship to each other, compar- 352/19, 20 ing the first and second signals to produce a control signal, and controlling one of the first'and second [56-] drive means to maintain the control signal at a UNITED TA PATENTS predetermined vah e, indicating a synchronous move'-' ment of the two strips.

2,679,l87 5/1954 Hitting....................................352/l7 PATENTEDHARZTISH SHEET 010E 11 F'IG.I

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PATENTEma-arzzims SHEET [19 0F 11 PATENTEDMAR 2 7197s SHEET 10 OF 11 AUTOMATIC SYNCHRONIZATION OF TWO STRIP DRIVES This invention relates to a process of synchronizing two drive means, particularly to a process of synchronizing a motion picture-handling appliance and g a sound tape-handling appliance, in which process a first signal is associated with different length portions of at least one strip and when this strip is moved in synchronism with a second strip said signal is compared with a second signal which is generated during such movement. The invention relates also to an apparatus and an appliance for use in carrying out the process.

Numerous different synchronizing processes have been disclosed. A synchronous movement requires not only that the two drive means operate at corresponding velocities but the phase angles must also be the same. All systems which synchronize only the velocities have the disadvantage that there is no correct phase coordination. It is particularly difficult to maintain a proper phase coordination when the drive means run up or slow down. Whereas it is already known to synchronize a film strip and a sound tape with the aid of perforated sound tapes, which are driven by sprockets, that system has the important disadvantage that perforated sound tapes are available only with difficulty. A synchronization by means of a pilot tone may also permit of phase errors because the pilot tone signals are equal so that a proper phase coordination of the picture and the associated sound can be re-established only with difficulty when one or more signals have failed to appear. This remark is also applicable to those systems in which the absolute number of pulses is stored and the stored pulses derived from each strip are compared. Whereas it has been attempted to avoid these disadvantages by the use of additional signals, such as start marks, the errors have remained relatively large in the known systems. in connection with the cutting of picture and sound tapes it has already been proposed to number the several picture and sound sequences by means of Morse characters so that even after a loss of one of those characters there will also be a proper phase coordination of the picture and sound. Unfortunately, it has not been possible to use this system or synchronizing two drive means because the signals are complicated and can be automatically read only with difficulty.

All these disadvantages are eliminated according to the invention in that both signals have at least one parameter of variable magnitude, preferably different frequencies, suitably in a sequence which is ordered by magnitude, these parameters are present at least in portions of the overall length of the associated strip and preferably in portions which correspond to each other as regards the period of the signals, the parameters of the two signals have a predetermined functional relationship and the comparison of these two signals during the movement of the strips results in a control signal having a predetermined and preferably constant, desired magnitude. Hence, the invention provides signals which are associated with the two drive means and which in different length portions have at least one parameter of varying magnitude so that the respective magnitude of the parameter represents a numbering of the associated length portion. The parameter may consist of the amplitude or preferably of the frequency of the signal. The signal need not be a sound signal but may consist, e.g., of light signals. Whereas any desired code may be used to number the strip length portions, it will be desirable to order the variable parameter with increasing or decreasing magnitude. If the functional relationship between the parameters of the signals associated with the two drive means is known, a control signal which during a synchronous movement has a predetermined, desired value can easily be derived by a comparison of the two signals during the movement of the strips. As will be discussed with reference to the drawings, it will be desirable if this desired value is constant. The desired value may vary between two different levels. Whereas the periods of the two signals may differ, they will preferably have equal periods. Because a sufficient number of parameter values which can be exactly differentiated is not available for a relatively large length of the strip, it will generally be impossible to provide different parameter values throughout the length of the respective strip. it has been found that it is entirely sufficient if the two signals have a variable parameter in portions of the overall length of the associated strip. If this is the case and one of the strips, in most cases the film, does not carry the signal which is associated with it, an additional signal will suitably be recorded for each signal period on this strip at a predetermined point, e.g., at the beginning or end of the period. Various means for recording signals on films are known and apparent, e.g., from the Austrian Patent Specification 272,837. if a strip does not carry the signal which is associated with it, the correct phase coordination may not be readily established at the beginning of a recording or playback so that special steps are required for this purpose to enable an automatic coordination of the picture and sound recordings. This object is accomplished by the abovementioned additional signal, which is recorded, e.g., at the beginning of each period of the signal associated with the strip, particularly the film. When the appliance is switched on, the signal generator will then operate so that the additional signal recorded on the strip coincides with the predetermined part of the signal period.

Within the scope of the invention, the signals may be utilized in various ways. For instance, the signals which are associated with the two drive means may preferably be uniform and may be converted and/or amplified, if desired, and then be applied to a bridge circuit, e.g., a Wheatstone bridge, so that control signals will appear across the load impedance of the bridge in case of a deviation from a synchronous condition. During a synchronous operation of the two drive means, there will be a zero difference between the parameters applied to the inputs of the bridge. In case of a deviation from a synchronous condition, a signal will appear across the load impedance of the bridge and may be used as a control signal directly or after inversion. In this embodiment, the parameter values of the two signals are continuously compared and a control signal is generated only in case of a deviation from a synchronous condition. In a preferred embodiment of the invention, the preferably frequency-modulated signals associated with the two strips may be amplified, if desired, and are then superposed, and the varying value of the resulting signal is detected and is used to derive a control signal having a magnitude which depends on the varying value of the resulting signal. The

use of frequency-modulated signals has the advantage that these signals are less liable to be deranged. The signals may consist of sound signals or light signals. The difference between the largest and smallest value of the parameter is preferably the same for each signal so that a proper superposition will result in constant desired values of the resulting signal during a synchronous movement.

Two particularly desirable embodiments may be adopted as regards the shape and variation of the signals. In one case, the changes of the parameter are the same for both signals and preferably in phase during synchronous movements. In this case, the two signals will preferably be superposed by subtraction. This results in one or two constant desired values during synchronous movements. To prevent that the subtraction results in a signal which has values that are too low or even negative, the difference between the parameters of the two signals preferably exceeds the difference between the largest and smallest values of the parameter of each signal.

The two signals may alternatively vary in such a manner that the parameter values of the two signals vary in mutually opposite senses but preferably in phase during synchronous movements, and the signals may then be superposed by addition. This method results also in constant desired values during synchronous movements and there is in this case no restriction as to the difference between the parameters of the signals. It has proved particularly desirable if the parameter values of the signal which is associated with the controlled drive means are ordered to increase in magnitude. When the controlled drive means moves faster than the controlling drive means, a phase difference between the frequency-modulated signals will be due not only to the difference in velocity but also to the fact that the higher velocity results in a higher frequency of the signals so that a phase displacement is indicated which has not been taken place in fact. This results in a highly desirable control response. For audiofrequency signals, the most desirable variable parameter values have been found to lie in a range between 250 and 5,000 Hertz, preferably between 500 and 2,500 Hertz.

In a desirable development of the invention, a control signal is derived from the resulting signal in that the varying value of the resulting signal is compared with at least two predetermined reference values, which are higher or lower than the desired value for synchronous movements by a certain amount, which is suitably equal for both reference values or may be zero. Where two desired values appear in alternation, one reference value may exceed the upper desired value by a predetermined amount or be equal thereto and the other reference value may be lower than the lower desired value. This takes the fact into account that the varying parameter of the signals associated with the two drive means results in a large variation of the value of the resulting signal and it is difficult to derive a control signal from a comparison of this greatly varying parameter value with a single reference value. The difference between the two predetermined reference values is preferably larger than or equal to the variations of the resulting signal during a deviation from a synchronous condition. In this case the resulting signal always varies about one of the two comparison values and both reference values may be used to generate the control signal. The reference values are suitably selected so that deviations of the resulting signal in the same sense from one of the two reference values and within the range of the possible deviations of the resulting signal result in control signals having the same sign. In other words, a parameter value which exceeds one reference value by a certain amount results in the same control signal as a parameter value which exceeds the other reference value by the same amount. This results in a simplified circuit for controlling this process. If the signals associated with the two drive means are in phase, the desired value itself may be used as a third reference value in addition to the two reference values mentioned above so that the two other reference values are suitably selected to correspond to a deviation of one-half period from a synchronous condition.

In recording or reproducing appliances for striplike information carriers, particularly motion picture appliances which comprise a film-driving transmission and a synchronizing signal generator formed by a preferably disclike sound carrier, a certain problem arises during the starting situation at the beginning of a recording on a new film and the beginning of the reproduction when the film must be threaded into the appliance. The problems which will be described hereinafter may also arise, theoretically, in a sound tape-handling appliance but this is not normally the case. These problems are due to the fact that it is not ensured at the beginning of a recording or reproduction that the synchronizing signals associated with the two drive means to be synchronized are initially in phase. It has already been proposed to record a further signal for each period of the synchronizing signal, e.g., at the beginning of each period. This additional signal serves to lock in the associated signal. The combination of those features of the invention which have been described hereinbefore affords the advantage that the synchronizing signals are properly coordinated within very short time. It is not the purpose of a synchronizing process, however, to compensate coordination errors which arise at the beginning of a recording or reproduction. When these coordination errors, which are virtually due to the fact that the starting position of the signal generator is not defined, are succeeded by an irregular operation of the drive means, the synchronizing means may not be capable of performing the control functions to be accomplished. Actually, the synchronizing means serve only to compensate irregular movements or displacements which are due to an elongation of the strip or the like.

The invention provides for an improvement by the use of means for adjusting the sound carrier to a predetermined position, which means are preferably connected to the mode control switch. This measure relieves the synchronizing means from control functions which may be required as a result of an undefined and undefinable position of the sound carrier at the beginning of a recording or reproduction. The term mode control switch used in this connection may include also, e.g., a camera release member because this is also a mode control switch. Preferably in connection with cameras having a release switch, it is possible to use within the scope of the invention an arrangement in which the sound carrier is operatively connected to a by-pass switch, which by-passes the interrupter for the motor of the appliance. In this case, the sound carrier is adjusted by the motor of the appliance until the sound carrier assumes its predetermined position even when the interrupter contacts have been opened. This may be accomplished if the sound carrier is provided with conducting surfaces, which may be printed on the sound carrier and which are interrupted at a point which corresponds to a predetermined position of the sound carrier. In a camera, the problem may be solved without need for additional electrical means. In this case, the sound carrier is preferably provided with a locking device for the release switch, which locking device is in locking position when the sound carrier is in a position other than the predetermined position. Under certain circumstances it may be undesirable for the movement of the appliance to be continued only in order to adjust the sound carrier to its predetermined position. In a camera, this may result in a waste of film. For this reason, it is a feature of the invention to connect the mode control switch, preferably the release switch, to means for disabling the intermittent strip drive means, e.g., for disengaging a pull-down claw, which means are in operative position when the mode control switch is in position OFF. Means for disabling an intermittent strip drive means are known for other purposes in the form of clutches or of means for disengaging a pull-down claw. When a camera which is provided with such means is stopped and the sound carrier does not assume its predetermined position, only a single picture can be overexposed as a result of a rotation of the shutter. Even this defect may be eliminated if the mode control switch is connected to an auxiliary shutter, known per se, which blocks the light path of the lens when the mode control switch is in position OFF. Because an auxiliary shutter is moved into the path of light of the lens when the appliance has been shut off, the main shutter may move for any time whatever without causing an overexposure in a camera. In a projector, such auxiliary shutter must be disposed behind the aperture plate to block the light emitted by the lamp. In a projector, this auxiliary shutter may consist ofa heat filter.

In an alternative solution which may be adopted to solve the problem outlined above, the mode control switch is connected to an actuating means for a clutch, which is connected between the main drive means of the appliance and the shutter and preferably to an actuating means for a clutch which is connected between the main drive means of the appliance and the intermittent strip drive means. In this case, the main drive means of the appliance may act only on the means for driving the sound carrier rather than the intermittent strip drive means and/or the shutter.

In another arrangement, which is particularly suitable for projector appliances, the sound carrier is adapted to be uncoupled from its drive means, preferably by the mode control switch, as it moves to position OFF. In a projector, individual parts, such as the sound carrier may be accessible more easily than in a camera. If the sound carrier can be uncoupled from its drive means, it may be moved, e.g., by hand, to its predetermined position. This operation may be performed automatically if spring means for returning the sound carrier to its predetermined position are connected to the sound carrier.

Additional features of the invention will become apparent from the following description of the process according to the invention and of several embodiments shown by way of example.

FIG. I is a diagrammatic view which illustrates the process according to the invention carried out by means of'a camera designed according to the invention.

FIGS. 2A to 5A show the coordination of two signals.

FIGS. 28 to 5B represent the signals which result from this coordination.

FIGS. 6 and 7 illustrate the step carried out according to the invention to utilize the resulting signals.

FIG. 8 shows an arrangement for carrying out the process according to the invention.

FIGS. 9 to 14 are diagrams showing different embodiments of a circuit which comprises a Schmitt trigger.

FIG. 15 is a diagram which represents the switching function.

FIGS. 16 and 17 are views showing illustrative motor control circuits. a

A comparison means for deriving the control signals is shown in FIG. 18.

FIG. 19 shows a circuit arrangement for carrying out the process according to the invention with the aid of a differential amplifier.

FIG. 20 shows a simplified embodiment in an appliance which is designed in accordance with Austrian Patent (A 6112/).

FIGS. 21 to 23 illustrate modifications embodied in a camera designed according to the invention.

FIG. 24 illustrates another embodiment.

FIGS. 25 and 26 show a modified arrangement in FIG. 25 in a side elevation and in FIG. 26 in a top plan view partly in section.

The invention relies on the use of a certain kind of signals which are associated with the drive means to be synchronized. Four possible forms and coordinations of the signals will be described hereinafter'with reference to FIGS. 2 to 5. It may be stated at this juncture that a first signal may be provided, e.g., on the sound tape 1 of a sound tape-handling appliance 2 before a recording is made on said tape. During the operation of the sound tape-handling appliance 2, the signals applied to the tape 1 are detected by a sound head or the like (not shown) and fed to a synchronizing device 3. The camera release of a camera 4 is operated at the same time. The film, not shown, is contained in a cartridge 5, which is indicated in dotted lines and contained in the camera. This is usual in cameras. The take-up reel in the camera is driven by a shaft 6. Theoretically, signals like those on the sound tape 1 could be applied also to the film. Because this is difficult in practice, the signals on the film may be replaced by signals generated by a signal generator, which is controlled in dependence on the velocity of the film in the camera 4.

According to FIG. 1, that signal generator consists of a gear 7, which is secured to the shaft 6, a gear 8 in mesh with the gear 7, and a disc 9,-which is driven by the gear 8 and in which the signal is stored which is to be associated with the film. It is desirable to use the disc 9 because only a small space is available in a camera 4 and because a disc can be relatively easily arranged within the space which is provided in the camera 4 for the cartridge. A signal-detecting means, not shown; must also be contained in the camera. The nature of this signal-detecting device will obviously depend on the form in which the signals are stored on the disc 9. If the signals are stored magnetically, a suitable sound head will be provided. Where a gramophone record is used, a suitable tone arm will be used. If the disc 9 stores the signal in the form of an optical sound recording, a detector for such optical sound recording will be provided in the camera 4. If the disc 9 consists of a gram'ophone record or contains the signal in the form of a stylus-cut sound recording, the recording may become worn off so that the disc 9 comprises preferably a plurality of closed signal tracks, with which the pick-up can be selectively aligned. When one of the tracks has been worn off, a suitable shifting device may be operated to align the pick-up with another track, which has not yet been worn.

The signals which have been derived from the disc 9 are also fed to the device 3, in which the signals from the tape 1 and those from the disc 9 are compared to derive therefrom a control signal for the camera motor. Because the synchronizing signals associated with the film are not carried by the latter but are generated by a signal generator which operates in synchronism with the movement of the film, it is desirable for the reproduction to ensure from the beginning that the signals of the strip 1 are in phase with those derived from the signal generator. For this purpose, the camera 4 has suitably a known marking device, which causes at least one additional signal to be recorded on the film for each period of the signal derived from the disc. This additional signal is timed, e.g., to appear at the beginning of each period of the signal derived from the disc 9. For this purpose, a device may be used, e.g., which is similar to the one shown in the Austrian Patent Specification No. 272,837. This device may be adapted for use in carrying out the present invention in that the shutter for the marking light path is operated in dependence on the velocity of the film. For instance, a cam may be provided, which is coaxial to the gear 8 and which during each revolution of this gear and of the disc 9 opens the shutter for the marking light path at least once.

The previous and subsequent parts of the description are based on the assumption that audiofrequency signals, particularly at different frequencies, are generated. On principle, light signals at different frequencies or signals which differ in amplitude may also be generated.

FIGS. 2A, 3A, 4A and 5A show the coordination of the two signals. The signal indicated in thin lines may be the signal which is recorded on the tape 1 and the signal represented in thick lines may be the signal from the camera 4. In the diagrams, time is plotted on the axis of abscissae and frequency on the axis of ordinates. It is apparent that the signals associated with the two drive means have a parameter, namely, frequency, which has a value that varies with time. In the embodiments shown by way of example, the signals are rampshaped although different forms of signals may be used. The signal period, i.e., the time in which the value of the variable parameter of the signal rises from its smallest value to its highest value, may correspond to the entire length of the tape 1 or of the film contained in the cartridge 5. This would have the advantage that a specific parameter value of the signal would be associated with each point of the length of the respective strip. In that case, the coordination of the two signals could easily be detected. On the other hand, with such a long period the difference between the highest and lowest values of the parameter of the signal must be very large so that the signal detectors in the sound tapehandling appliance 2 and the camera 4 must be responsive within a fairly wide range. Unless this is possible, the parameter values increase only with a rather flat slope so that the signal detectors must have a very exact function if the differences between the parameter values should be recognized. It has been found that with frequency-modulated signals the audiofrequency ranges suitably from 2505,00 Hertz, preferably SOD-2,500 Hertz, in view of the requirements met by inexpensive commercially available tape recorders.

In the drawing, FIGS. 2 Au, 3 Au, 4 Aa and 5 Aa represent various forms in which two signals can be coordinated during synchronous movements. As has been mentioned above, the signal S represented by thin lines is the signal coming from the sound tape 1 whereas the signal S, represented by thick lines is the signal from the camera 4. The diagrams shown in column b represent a condition in which the signal S, from the camera leads the signal S from the sound tape so that the period of signal S, is terminated earlier than during synchronous movements. The diagrams in column 0 represent a condition in which the film lags the sound tape so that the period of signal S, terminates later than during synchronous movements.

According to FIG. 2, signals 8,, S, uniform or similar and in phase so that they are in phase also during synchronous movements. The frequencies of these signals are ordered by magnitude so that a ramp signal results. The parameter values could be arranged in accordance with any desired code but this will result in difficulties when these signals are processed to form a control signal.

To enable the generation of a control signal, the signals shown in FIG. 2 may have equal parameter values during synchronous movements (FIG. 2 Aa) and the signals may be applied to a comparator, e.g., a bridge circuit, in which no output signal appears across the load impedance whereas a deviation from a synchronous condition results in a signal which has a sign depending on the direction of the deviation and appears across the load impedance.

In another, preferred embodiment, the two signals 8,, S, are first superposed to form a resulting signal from the two signals 8,, S,. If the two signals 8,, S, are similar (FIGS. 2, 3), the resulting signal will have a desirable waveform if the signals 8,, S, are subtracted one from the other. It is clearly apparent from FIG. 28 that the difference between the signals S, and S, is always the same during synchronous movements, as is shown in FIG. 2A so that synchronous movements result in a resulting signal S, having a uniform magnitude. An addition of the signals 5,, S, having the configuration shown in FIG. 2 would result in a resulting ramp signal which has inclined edges that are twice as steep as the inclined edges of the signals S, and 8,. Such resulting signal could also be used to control drive means but additional means would be required for this purpose. For instance, a variable resistor could be used which is varied in synchronism with the rotation of the controlling drive means to compensate the pulsation of the resulting signal.

A phase difference between the signals associated with the two drive means may be due to a mere phase displacement or to an operation of the two drive means at different velocities and results in a coordination of the two signals 8,, 5,, such as is apparent from FIGS. 2 Ab and 2 Ac. The use of frequency-modulated signals affords the advantage that the higher velocity simulates or actually results in a higher frequency so that an increase of the velocity of the film simulates a phase lead relative to the sound tape when the signal associated with the controlled camera drive has frequency values which are ordered with increasing magnitude. This results in a very good control response which virtually precludes hunting. A lead of the camera relative to the sound tape results in a resulting signal 8,, which may have negative values if the frequency difference between signals S, and S, is small during synchronous movements (FIG. 2 Aa). This may be avoided in that the difference between signals S, and S, during synchronous movements exceeds the difference between the highest and lowest parameter values of one of the two signals. As is apparent from FIGS. 2 Ab and 2 A c, deviations from a synchronous condition result in different resulting signals S, and S,, which appear in alternation. These signals may differ only slightly from the resulting signal S, for synchronous movements and in this case have a large pulse width, or they may differ greatly from the resulting signal S, and in this case have a small pulse width. If the signals S, and S, differ in phase by 180, the upper and lower values of the resulting signal differ from the desired value of the signal S, by equal amounts. The resulting waveform is apparent from FIG. 3 Ba.

In the coordination shown in FIG. 3, the signals 8,, S, differ in phase by 180 during synchronous movements, so that this condition results in a resulting signal S, having two different values in alternation. A comparison of this signal S, with the signals S, and S, which result in the case of a deviation from a synchronous condition will show that the upper value of each of the signals 8,, S, differs only relatively slightly from the upper value of signal S,. The same remark is applicable to the lower values. This result is due to a suitable steepness of the inclined edges of signals 8,, 8,. As a result, the difference between the upper and lower values of signal S,

exceeds the differences between the upper and lower values of signals 8,, S, and the respective upper and lower values of the signal S, in the case of a deviation from the synchronous condition. This fact facilitates the generation of a control signal, as will be described hereinafter with reference to FIG. 7.

FIG. 4 represents a condition in which the signals S, and S, are in phaseduring synchronous movements but their frequency values vary in mutually opposite directions. It is apparent from FIG. 4 Aa that the difference between signals S, and S, decreases continuously during a signal period. If the two signals were superposed with subtraction, the resulting signal would be a ramp signal like that formed by an addition of the signals in the embodiments shown in FIGS. 2 and 3.

With signals which have mutually oppositely directed characteristics it is desirable for this reason to superpose the two signals with addition. In this case, the resulting signal S, during synchronous movements will be uniform whereas the signals 8,, S, obtained in case of a deviation from the synchronous condition will be similar to those represented in FIG. 2.

These remarks are substantially applicable also to FIG. 5, in which the signals 5,, S, have also mutually oppositely directed characteristics and during synchronous movements are offset l from each other. In this case, the resulting signals obtained by an addition ofsignals S,, S, are similar to those obtained in the embodiment shown in FIG. 3.

FIGS. 2 to 5 represent in four typical examples how signals can be chosen and coordinated. All other embodiments can virtually be derived from the embodiments shown by way of example. For instance, sinusoidal signals could be used rather than ramp signals. This would substantially mean that similar signals having opposite signs are used in alternation. If the signals are out of phase during synchronous movements (FIGS. 3, 5), the phase difference need not be but virtually any desired phase difference may be selected.

An embodiment of the process according to the invention may be explained with reference to FIG. 6. The resulting signals represented according to FIG. 4 are shown in the right-hand portion of the diagram. The signal S, is represented by a solid line, the signal S, by a dotted line and the signal S, by a dash-dot line. These different resulting signals which may appear are compared with at least two reference values, namely, an upper reference value Ow and a lower reference value Uw. In addition, the resulting signals are compared to a desired value Sw for synchronous movements. This value Sw corresponds in magnitude to the resulting signal S,. The two other reference values Ow, Uw correspond respectively to the upper and lower values of a signal which is i180 out of phase or may be different although they suitably correspond to a deviation which corresponds to a lead or lag of the controlled drive means by 360 (S,+S,). It is apparent that the upper value of the resulting signal S, which results during a lead of the camera differs from the upper reference value Ow by the same amountby which its lower level differs from the lower reference level Uw. The same remark is applicable to the signal S, so that when the resulting signals are suitably filtered and compared with the reference levels Ow and Uw or Sw it can easily be ascertained whether the controlled drive means leads or lags or is synchronized.

Similar remarks are applicable to the embodiment shown in FIG. 7, in which the signals 8,, S, and S, are selected in accordance with the embodiment shown in FIG. 5. During synchronous operation, two values appear in alternation and in this case the two reference values Ow, Uw are equal to these two values of the signal 8,. As has been mentioned hereinbefore, the signals 8,, S, have been selected so that the difference between the upper and lower values of the resulting signal S, is larger than or equal to the deviations in the resulting signal which are due to a deviation from a synchronous condition. It is found in fact that the upper values of signals 8,, S, are near the upper reference value Ow whereas the respective lower values differ distinctly from the upper reference value Ow and are near the lower reference value U w. By a suitable filtering it can also easily be ascertained whether the values of the resulting signal are aboveor below the reference values.

FIG. 8 shows an arrangement for carrying out the process according to the invention. The inputs for the signals 8,, S are shown in the upper left portion of FIG. 8. The signal S is directly applied to an amplifier 10. The signal 8,, may be compared first with a non-modulated reference signal S if the signal generator comprising the disc 9 (FIG. 1) in the camera 4 has the signals stored therein in the form of a stylus-cut sound recording or comprises a gramophone record. In this case, the sound pick-up is sensitive to shakes so that a shake may result in an interfering signal, which may disturb the synchronizing control and must be filtered out. This is best accomplished in that a non-modulated reference signal S is recorded on the disc 9 at the same time as the frequency-modulated signal S so that any shake will result in the same disturbance of the signal S and of the reference signal S In a gramophone record, the sound grooves are preferably like those for stereophonic sound recordings in such a manner that the modulated signal is recorded on one side and the non-modulated signal is recorded on the other side of the groove. The signals S 8,; may then be applied to a differentiator 11, in which the interfering signal is filtered out. The differentiator 11 may be omitted if the signal S, has been recorded by a different method. In this case the signal S from the camera is directly applied to an amplifier 12. The outputs of the amplifiers 10, 12 are connected to a heterodyning circuit 13, in which the resulting signal is formed. Because the signals 5,, S are frequency-modulated signals, the resulting signal must be applied to a frequency-identifying circuit 14, which has at its input a frequency converter 15, which virtually constitutes a frequency counter because it generates a pulse in response to every change of the parameter of the resulting signal from the upper value to the lower one. Hence, each pulse of uniform width which is generated by the frequency converter 15 corresponds to a pulse of the resulting signal, regardless of the width of the latter pulse. As a result, the control signal to be formed is independent of the pulse width of the resulting signal. The frequency converter 15 has connected to it a comparator circuit 16, which comprises at least two and in the present embodiment three channels and which in the present embodiment serves also as a frequencyvoltage converter. For this purpose, a threshold value switch 17a, 17b or 17c is provided at the outlet end of each channel. These threshold value switches have preferably a hysteresis which is smaller than the residual ripple at the input. Each of the three channels is tuned to a predetermined frequency by a suitably dimensioned resistancecapacitance circuit. For instance, a channel 16 a is tuned to 2 kHz, a channel 16b to 3 kHz and a channel 16c to 4 kHz. The value of 2 kHz in channel 16a corresponds to the lower reference value Uw of FIG. 6, the value of 3 kHz in channel 16b corresponds to the desired value Sw and the value of 4 kHz in channel 160 to the upper reference value Ow. The outputs of the three channels 16a, 16b, 16c are applied to an identifying logic circuit 18, which generates a control signal that is applied to a motor control circuit 19 disposed in the camera.

In the embodiment shown by way of example, the motor control circuit 19 consists of a current-voltage control circuit. Such control circuits are known per se. A modified form for use within the scope of the invention will now be described. The motor control circuit 19 comprises in known manner a transistor 20 for controlling the motor 21. The base of the control transistor 20 is controlled by a comparison transistor 22. A voltage divider is connected to the base of the comparison transistor 22. It has how been found that the control signal delivered by the logic circuit 18 to an input transistor 23 of the motor control circuit is preferably applied to one section of the voltage divider which is connected to the base of the comparison transistor 22.

This section comprises a relatively small resistance 24. A capacitor 26 is connected between the reference input 25 for the control signal and the base of the comparison transistor and is dimensioned so as to reduce the time lag of the response to the control signal. The capacitor 26 may be adjustable. The voltage stabilizin g circuit connected between the output of the control transistor 20 and the motor 21 is of known type.

In the description of FIG. 8 ithas been stated in connection with the threshold value switches 17a, 17b, 17c that they should have a hysteresis which is smaller than the residual ripple at their input. It has now been found that this object can be well accomplished by a Schmitt trigger, such as is shown in FIG. 9. This Schmitt trigger comprises in the usual manner an input transistor 27 and an output transistor 28. A difference from known circuits resides in that regeneration is accomplished by a resistor 29, which is connected between the base of the input transistor 27 and the collector of the output transistor 28. The two transistors 27, 28 are complementary transistors. The input transistor 27 is a PM? transistor and the output transistor 28 an NPN transistor. The hysteresis of the Schmitt trigger which is shown may be adjusted by means of the resistor 29, which is connected to the base of the input transistor 27, or another variable resistor 30, which is connected to the base of the transistor 27. A voltage divider consisting of two resistors 31, 32 is included in the emitter circuit of the input transistor 27 and serves to adjust the threshold value. I

The voltage divider which is included in the emitter circuit of the input transistor 27 comprises in that section which comprises the resistor 32 also a diode D for compensating any voltage and temperature changes at least in part. The resistor 32 may be replaced by a series of diodes. If the voltage controlled by the diode D is designated U,,, the following calculation may be performed: W

U Rad/F D) 5 31 so that the proportionality of the voltages U and U is improved.

In many cases it is desirable to compensate voltage and temperature voltage alterations not only in part. In

this case, an arrangement such as is shown in FIG. 10 may be adopted, where parts having the same function are provided with the same reference character. A difference resides virtually only in that the emitter circuit of the input transistor is connected by a resistor R to the positive terminal of the power source, not shown and includes an emitter follower T the base of which is controlled by the voltage divider consisting of the resistors 31, 32 so that and the operating voltage U, is.very well compensated and always proportional to the threshold voltage U,.

FIG. 11 shows an embodiment which is similar to that of FIG. but comprises homopolar transistors so that the resistor R is grounded. In practice it will'be necessary in such circuit to provide a diode circuit between the collector of the input transistor 27 and the base of the output transistor 28. In the present case, this diode circuit consists of a single Zener diode D,. A circuit such as that of FIG. 10 might also comprise homopolar transistors if one or more diodes are connected between the collector of the input transistor and the base of the output transistor. If it is desired for any reason whatever to use PNP transistors rather than the NPN transistors which are shown, this may be enabled by reversing the polarity of the operating voltage U,,. This measure would enable also a replacement of the transistors 27, 28 shown in FIGS. 9 and 10.

When the circuit should be energized in response to a predetermined threshold voltage and de-energized in response to a threshold voltage which is higher than the first, this may be accomplished by a circuit such as is shown in FIG. 12. The same includes an additional transistor T the base of which is connected to a voltage divider, which shunts the input transistor and consists of two resistors R R The emitters of the two transistors 27, T are interconnected. In this case, a first threshold voltage initially renders the Schmitt trigger conducting but a further voltage rise up to a second threshold value blocks the input transistor 27 because the voltage divider R R is connected to the base of the input transistor 27. The corresponding modifications comprising homopolar transistors 27, 28, T is shown in FIG. 13, where the base of the transistor T is also connected to the base of the input transistor 27 by the voltage divider R R and the emitter of the transistor T is connected to the emitter of the input transistor. A Zener diode D is provided as in the embodiment of FIG. 1 1.

For the sake of clearness, the FIGS. 12, 13, and 14 show greatly simplified embodiments, in which compensating circuits are omitted.

The switching function of the embodiment shown in FIG. 14 is an inversion of the function of the Schmitt trigger shown in FIG. 12. The only difference resides in that the input is connected in known manner by the series resistor 30 to the base of the input transistor 27' rather than to the additional transistor T The switching functions of this embodiment and of the remaining embodiments will not be explained with reference to FIG. 15.

The input voltage U, represented by a thick line exhibits a linear rise. The thin line represents an output voltage U such as is produced in the circuits shown in FIGS. 9 to 11. An embodiment as shown in FIG. 12 or 13 has such a switching function that the output voltage initially follows the output voltage U to a certain value. This means that with a low input voltage the output voltage is virtually zero and rises virtually to the full operating voltage when a predetermined threshold voltage is exceeded. In response to a further increase of the input voltage, the Schmitt trigger is reset to its initial condition. The resulting changes of the voltage U are indicated by a dotted line.

In a circuit as shown in FIG. 14, a lower input voltage U, results in the output voltage U which is represented by a dash-dot line and above a predetermined threshold value is returned to zero. The output voltage will respond like the output voltage U to a further rise of the input voltage.

Numerous modifications are possible within the scope of the invention. For instance, homopolar transistors could be used in the embodiment of FIG. 14 if the input is applied directly to the base of transistor T It has already been mentioned that numerous circuits may be used to compensate various influences. The Schmitt trigger according to the invention is not only particularly suitable for a circuit according to FIG. 8 but may be used with all circuits which are required to have functions similar to those described hereinbefore. Another use of the described circuit will be described with reference to FIG. 16.

FIG. 16 shows a modification of the motor control circuit 19 shown in FIG. 8. The motor control circuit 19 could be described as a current-voltage control circuit whereas the control circuit shown in FIG. 16 must be described as a pulse control circuit. This circuit is used to control a motor 33 in a camera, which comprises also a zooming motor 34. The motor 33 is connected to a speed-controlled change-over switch 35 at one input of the control circuit. This change-over switch 35 is connected to the input of a frequency-voltage converter, which comprises a transistor 36. The output of this converter is connected in the usual manner to a smoothing capacitor 37, which may have only a relatively low capacitance and in this respect differs from the conventional circuits. In the known circuits of this kind it is desired to provide at the output of the frequency-voltage converter a voltage which is as smooth as possible. It has now been found that the residual ripple at the output of this converter may be used to control the motor. For this purpose, the frequency-voltage converter has connected to it a threshold value switch consisting of a Schmitt trigger which is of the type shown in FIG. 9 and comprises an input transistor 27' and an output transistor 28. For regeneration, a resistor 29 is connected between the collector of the output transistor 28 and the base of the input transistor 27. Matching is accomplished by an adjusting resistor 38. It has already been mentioned that a voltage divider adjusting the threshold value is included in the emitter circuit of the input transistor 27'. This voltage divider comprises an adjustable resistor 39. The control signal from the logic circuit 18 (FIG. 18) is applied via an input terminal 40 to this voltage divider. The output of the Schmitt trigger is coupled to the motor 33 by a conventional switching circuit which comprises a transistor 41 so that the motor 33 is fed with current pulses which have a width that varies in accordance with the reference signal that has been applied.

A modified motor control circuit is shown in FIG. 17 and easily enables the operation of the motor at a constant speed and with a high efficiency. Another advantage of this circuit is that it is simple and inexpen- SIVC.

The camera motor 33 comprises a commutator, which constitutes a change-over switch at the input of the circuit. The change-over switch 35 is included in a frequency-voltage converter 53 and applies square wave signals thereto. The frequency-voltage converter produces an output voltage 54 consisting of a d.c. voltage which varies with the frequency that is applied and on which an ac. ramp voltage is superposed. It is significant that the speed is controlled by a circuit fed with an a.c. voltage which has a frequency that depends on the speed of the motor 33. This object may be accomplished by circuits which are different from the circuit 53 which is shown. In known motor control circuits, the output of the frequency-voltage converter is as smooth as possible. This requirement is intentionally dropped in the practice of the invention, where the residual ripple is utilized for control functions. For this reason the capacitance of the capacitor 37 included in the output circuit of the frequency-voltage converter 53 may be relatively small. The output voltage of the frequencyvoltage converter 53 may be applied to a terminal 55 and may be used for different control functions, e.g., for a control of the diaphragm in response to the speed of the motor. This will ensure a uniform exposure even when the speed of the motor varies. The output circuit of the frequency-voltage converter 53 includes also a variable resistor 38 for adjusting purposes.

To enable a utilization of the residual ripple of the output signal 54, the frequency-voltage converter 53 has a threshold value switch 56 connected to it, which has a small hysteresis and which is continually reversed within the operating range by the residual ripple of the signal 54. The magnitude of the d.c. component in the signal 54 will depend on the speed of the motor 33 so that the peaks of these ramp pulses will exceed the threshold value of the switch 56 by an amount which depends on said d.c. voltage. Because the ramps of signal 54 necessarily have an inclined edge, the threshold value switch will remain closed and opened for a longer or shorter time depending on the amount by which the ramp peaks exceed the threshold voltage so that the output signal of the threshold value switch 56 consists of pulses having a width which depends on the input signal to the switch 56.

The threshold value switch 56 consists preferably of a Schmitt trigger, as shown, and in conventional manner comprises an input transistor 27' and an' output transistor 28. The circuit differs from a conventional Schmitt trigger in that regeneration is accomplished by a coupling resistor 29, which is connected between the base of the input transistor 27' and the collector of the output transistor 28. This regeneration results in a much steeper characteristic of the Schmitt trigger so that the hysteresis may be as large as 100 millivolts. A variable series resistor 30' is connected to the base of the input transistor 27 so that the hysteresis is determined by the ratio of the series resistance 30 to the coupling resistance 29. The hysteresis of the Schmitt trigger 56 can easily be adjusted if the resistors 29, 30' consist of variable resistors.

The response of the Schmitt trigger 56 and consequently the desired speed of the motor can easily be adjusted by the potentiometer 29', which is included in the emitter circuit of the input transistor 27.

It is seen that the potentiometer 29' is connected by the emitter follower T to the emitter circuit of the input transistor 27'. The emitter follower T serves to compensate voltage and temperature changes. This compensation is particularly important with camera motors. A reference signal may be applied to an input terminal 57 so that the potentiometer 29' may be used to set the number of frames per second in a camera. The control signal for synchronizing the camera motor with a sound tape-handling appliance is applied to the 'terminal 57.

An approximately trapezoidal signal 58 appears at the output of the Schmitt trigger 56. This signal 58 could be theoretically used to control the motor but in this case the Schmitt trigger 56 would have to be much more complicated. With the circuit which is shown, the output signal is too weak for a direct control of the motor. For this reason it is desired to connect the output of the Schmitt trigger 56 to a further switching circuit 59, which comprises a transistor 41 and a diode D connected to the base of the transistor 41. The switching circuit 59 serves for a current amplification of the signal 58 from the Schmitt trigger 56 and to generate pulses having steeper edges. The output signal 60 of the switching circuit 59 consists in fact of square wave pulses. Because the pulses have such steep edges, the transistor 41 may be used strictly as a switch so that a high efficiency is obtained. The motor 33 is de-energized and energized in alternation in response to the pulses 60. A change of the actual speed of the motor 33 results in a change of the pulse ratio and may result in a continuous blocking or conduction of the transistor 41.

In connection with FIG. 2 it has already been pointed out that the two signals 8,, S, associated with the sound tape 1 and the motion picture appliance 4 may be identical during synchronous movements and that a control signal can then be derived from a comparison of the two parameter values. One way in which such signals may be compared is shown in FIG. 18, where the signals 8,, S applied to the input of a Wheatstone bridge 42. When the parameter values of the two signals are equal, the bridge 42 is balanced so that no output signal will appear across the load impedance of the bridge circuit 42. Output signals having one sign or the other indicate a lead or lag of the controlled drive means. The output signals of the bridge circuit 42 may then be processed to form a control signal in various ways. According to FIG. 18, the load impedance of the bridge circuit 42 comprises a measuring instrument 43, which varies a capacitance 44 included in an ac. circuit. The resulting modulated alternating current is fed to a control circuit 45 for a motor 46 to control the latter. The instrument 43 may be replaced by a differential amplifier, the output signals of which are applied to a suitable motor control circuit.

An arrangement which comprises a differential amplifier is shown in FIG. 19. Each of the signals 8,, S is applied to a frequency-voltage converter, which comprises a transistor 47 or 47a and a smoothing capacitor 48 or 48a connected to the output of said transistor. The voltages which correspond to these two signals are 

1. A process of synchronizing first drive means for moving a first strip and second drive means for moving a second strip, which process comprises operating said first drive means to move said first strip generating a first signal in response to said movement of said first strip, operating said second drive means to move said second strip, generating a second signal in response to said movement of said second strip, each of said first and second signals having at least one varying parameter and are each associated with predetermined length portions of said first and second strips, respectively, which parameters have a predetermined functional relationship to each other, comparing said first and second signals to produce a control signal, and controlling one of said first and second drive means to maintain said control signal at a predetermined, desired value, which indicates a synchronous movement of said first and second strips.
 2. A process as set forth in claim 1, in which said first drive means is a motion picture appliance, said first strip is a film, said second drive means is a sound tape-handling appliance and said second strip is a sound tape.
 3. A process as set forth in claim 1, in which said first and second signals have said varying parameter in length portions of said first and second strips, respectively, which length portions correspond to each other as to the period of said first and second signals.
 4. A process as set forth in claim 1, in which said varying parameter is frequency.
 5. A process as set forth in claim 4, in which said frequency varies between 250 and 5,000 Hz.
 6. A process as set forth in claim 4, in which said frequency varies between 500 and 2,500 Hz.
 7. A process as set forth in claim 1, in which said parameter is ordered in accordance with its magnitude in each of said length portions.
 8. A process as set forth in claim 1, in which said one drive means is controlled to maintain said control signal at a constant desired value, which indicates a synchronous movement of said first and second strips.
 9. A process as set forth in claim 1, in which generating of at least said second signal is carried out by prerecording on said second strip and reproducing said signal from said strip as the latter is moved.
 10. A process as set forth in claim 1, in which each of said signals has a period which corresponds only to part of the length of the respective strip, said second strip has timing signals recorded thereon at a predetermined point of each signal period, said timing signals are reproduced from said second strip as the same is thus moved, and said second signals are generated in response to the reproduction of said timing signals.
 11. A process as set forth in claim 1, in which said signals are superposed to produce a resulting signal, said resulting signal is processed to produce an intermediate signal, which represents the comparison of said varying parameters of said first and second signals, and said intermediate signal is processed to produce a control signal having a value which corresponds to a varying parameter of said resulting signal.
 12. A process as set forth in claim 11, in which said first and second signals are frequency-modulated signals.
 13. A process as set forth in claim 11, in which the difference between the largest and smallest value of said varying parameter is the same in both of said first and second signals.
 14. A process as set forth in claim 11, in which said values of said first and second signals exhibit mutually opposite variations and said first and second signals are superposed with addition.
 15. A process as set forth in claim 11, in which said varying parameters of said first and second signals exhibit variations wHich are in phase during a synchronous movement of said first and second strips.
 16. A process as set forth in claim 15, in which said varying parameter of the signal associated with the strip which is moved by the drive means which is thus controlled increases with time.
 17. A process as set forth in claim 11, in which said first and second signals are amplified before they are superposed.
 18. A process as set forth in claim 11, which comprises providing at least two predetermined reference values, and comparing said resulting signal with said reference values to produce said control signal, at least one of said reference values differing from said desired value.
 19. A process as set forth in claim 18, in which one of said reference values is equal to said desired value.
 20. A process as set forth in claim 18, in which one of said reference values is an upper reference value which exceeds said desired value by a predetermined amount, and the other of said reference values is a lower reference value which is lower than said desired value by said predetermined amount.
 21. A process as set forth in claim 18, in which said desired value alternates between upper and lower levels one of said reference values is at least as high as said upper level, and the other of said reference values is lower than said lower level.
 22. A process as set forth in claim 21, in which said one reference value exceeds said upper level.
 23. A process as set forth in claim 18, in which said reference values differ by an amount which is at least as large as the deviations of said control signal from said desired value during the largest permissible deviation of the movements of said first and second strips from a synchronous condition.
 24. A process as set forth in claim 23, in which deviations of said resulting signal in the same sense from one of said two reference values within the range in which such deviations are permissible result in control signals having the same sign.
 25. A process as set forth in claim 1, in which said varying parameters exhibit equal variations in said first and second signals and said first and second signals are subtracted one from the other.
 26. A process as set forth in claim 25, in which said varying parameters are in phase during a synchronous movement of said first and second strips.
 27. A process as set forth in claim 25, in which the difference between said varying parameters of said first and second signals exceeds the difference between the highest and lowest value of said varying parameter of each of said signals.
 28. A process as set forth in claim 25, which comprises providing upper and lower reference values which are respectively above and below said desired value and comparing said resulting signal with said reference values and said desired value to generate said control signal.
 29. A process as set forth in claim 28, in which each of said reference values differs from said desired value by an amount which corresponds to a deviation of said movements of said first and second strips from synchronism by a length corresponding to one-half of the period of said first and second signals.
 30. A synchronizing arrangement for synchronizing first and second drive means for respectively moving first and second strips, which comprises a first signal deriving means for deriving a first signal associated with predetermined length portions of said first strip, a second signal deriving means for deriving a second signal in response to the movement of said second strip, each of said first and second signals having at least one varying parameter at least in portions of said signals which are associated with predetermined length portions of said first and second strips, which parameters have a predetermined functional relationship to each other, a superposing circuit having first and second inputs coupled to said first and second signal deriVing means, respectively, said superposing circuit being operable to superpose said first and second signals and to produce a resulting signal, a comparator which is arranged to receive said resulting signal and to derive a control signal therefrom, and control means adapted to control at least one of said drive means in response to said control signal.
 31. A synchronizing arrangement as set forth in claim 30, which comprises amplifier means for amplifying at least one of said first and second signals before the same is received by said superposing circuit.
 32. A synchronizing arrangement as set forth in claim 30, in which at least one of said first and second signal deriving means comprises means for reproducing signals recorded on said first and second strip respectively.
 33. A synchronizing arrangement as set forth in claim 30, in which said comparator comprises at least two channels.
 34. A synchronizing arrangement as set forth in claim 33, in which each of said channels comprises a threshold value switch.
 35. A synchronizing arrangement as set forth in claim 34, in which said superposing circuit is arranged to produce a resulting signal having a predetermined ripple and said threshold value switch has a hysteresis which is smaller than said ripple.
 36. A synchronizing arrangement as set forth in claim 33, in which each of said channels comprises a Schmitt trigger.
 37. A synchronizing arrangement as set forth in claim 33, in which said first and second signal deriving means are arranged to derive said first and second signals as frequency-modulated signals, said comparator comprises a frequency-identifying circuit having an input circuit which comprises a frequency counter, which is succeeded by said two channels, each of said channels is tuned to a predetermined frequency range, and at least one pulse-level converter is provided for converting pulses to a current having a corresponding value.
 38. A synchronizing arrangement as set forth in claim 37, in which said frequency counter comprises a frequency converter arranged to generate pulses which depend on the frequency of said resulting signal.
 39. A synchronizing arrangement as set forth in claim 30, which comprises a comparator circuit arranged to receive said control signal and to compare it with a predetermined value.
 40. A synchronizing arrangement as set forth in claim 39, which comprises a logic circuit coupled between said comparator and said comparator circuit.
 41. A synchronizing arrangement as set forth in claim 39, in which one of said drive means and said comparator circuit are incorporated in a motion picture appliance.
 42. A synchronizing arrangement as set forth in claim
 30. in which said superposing circuit comprises a bridge circuit.
 43. A synchronizing arrangement as set forth in claim 42, in which said bridge circuit comprises an operational amplifier.
 44. A synchronizing arrangement as set forth in claim 43, which comprises first and second frequency-voltage converters, which are respectively connected between said first and second signal deriving means and said amplifier.
 45. A synchronizing arrangement as set forth in claim 30, in which said one drive means comprises a motor and said comparator and control means comprises a direct current source having two terminals, a frequency-voltage converter arranged to be controlled by the speed of said motor and to produce an output having a predetermined ripple, a threshold value switch arranged to receive said output and having a hysteresis which is smaller than said ripple, a switching circuit adapted to control said motor, a switch adapted to be controlled by said motor and preceding said converter, at least one transistor included in said converter and having a collector and having a base connected to one of said terminals, a resistor connected between the other of said terminals and said collector, and an electric enErgy storage device connected between said collector and a point having an electric potential, said threshold value switch having a frequency-independent response.
 46. A synchronizing arrangement as set forth in claim 30, in which said one drive means comprises a motor and said control means comprise a motor control transistor having a collector, a comparison transistor for controlling said motor control transistor, said comparison transistor having a base, a voltage divider connected to said base and adapted to apply a first reference signal to said base, said voltage divider having a first section connected to said collector and a second section including an additional resistor which has a relatively low resistance, an output circuit which connects said collector to said motor to control the latter and comprises a voltage stabilizer, and a voltage source for applying a second reference signal to said additional transistor. 